L7: LIPIDS PROPERTIES

L7: Lipids properties

1. Introduction

Lipids are a heterogeneous group of compounds synthesized by organisms that are present in all biological tissues.

Like carbohydrates C,H and O are the principal elements of lipids althought oxygen content is much reduced.

 Lipids are made in general of long chains of hydrocarbons with realtively little oxygen. As a reault os this, they don't dissolve in polar solvents such as water.

In this experiment we are going to test solubility of different oils and how to identify lipids from a sample.

2. Objectives

• Test the solubility of lipids.
• Identify lipids in liquids compounds.
• Understand what are an emulsion and the effects of detergents.

3. Hypotesis

The hypothesis is to differentiate the reaction of water with different solutions.

4. Material

• test tube rack
• 250mL beaker
• water
• 6 test tubes
• cellulose paper
• dropper
• scissors
• glass road

• Olive oil
• soap
• milk with different fat content
• petroleum ether
• ethanol
• sudan III

5. Procedure

Solubility of some lipids:

First of all, we took 3 tubes test and we labeled them to differentiate which would have water, ethanol and ether. Each test tube we added 3 drops of oleic acid, then we put 1 mL of water, ethanol or ether according to the test tube.

Lipids identification:

       -  Translucent mark:

We caught two pieces of cellulose paper and we put a drop of water in one and on the other a drop of olive oil.

        - Sudan III dye:

We have prepared three test tubes with milk plus test water tube with the previous year, each test tube with a different milk (whole, semi-skimmed and without lactose), and we've put a drop of sweat III.

Permanent emulsion:

We put 100 mL of water in a 250 mL beaker. We have put 2mL oil and we have mixed. When we saw what was happening, we have put a few drops of soap and have seen the change.

6. Observations

In the first part we have seen that oil is insoluble in water. When ethanol is in contact with oil, it from micelles and ether can dissolve oil.

In the second part we have identifed the oil from a drop on a cellulose paper.

In the thord part we have tried to identify lipids with sudan III dye. Unfortunately this part of experiment didn't work.

In the fourth part we wanted to see how soh oil. When we added oil to water, it forned a monolayer in the sufare. When we added soap, molecules of oil are dispersed throughout the solution.

7. Conclusion

We can conclude that:

1. Oil is soluble in organic compounds like ether and insoluble in water.
2. Sudan III stairs lipids.
3. Lipids leave a translucent spot in cellulose paper.
4. When soap is added in a water and oil mixture, the soap molecules disperse oil throught the solution (permanent emulsion).

8. Questions

1. From your observation, which compounds can dissolve lipids?

The ether can dissolve the lipids.

2. Do the oil and water mix? what can you conclude about the polarity of the oil if you know that water is polar?

The oil is not soluble in water and remains in the top of the solution.

3. Why is liquid the olive oil at room temperature? and why not the lard?

Because the oil has a melting point much lower melting, since the chain C is smaller.

4. Why does a lipid leave a translucent spot on paper?

because it is greasy, contains lipids.

5. Which type of milk contains more lipids? why?

Whole milk because it contains all lipids having milk.

6. Did the oil and water mix when you added the soap?

It produces a permanent ebulltion.

7. What did the soap do to the fat?

That can not join again.

8. Can you think about process and locations were compounds like the soap would be important to an animal?

Bile acids.